Three-way catalysts containing at least one noble metal selected from among Pt (platinum), Pd (palladium) and Rh (rhodium) are widely used to clean exhaust gases discharged from internal combustion engines such as automobile engines. In a typical constitution of such a three-way catalyst, a catalyst coat layer is formed on a surface of a cylindrical honeycomb substrate, and one or two or more noble metals selected from among Pt, Pd and Rh are supported on the surface of the catalyst coat layer. When cleaning exhaust gas using such a honeycomb substrate, the exhaust gas is caused to flow into cells of the substrate from the exhaust gas inlet-side end, the exhaust gas is brought into contact with the catalyst coat layer formed on surfaces of dividing walls that divide the cells, and the exhaust gas is then discharged to the outside from the exhaust gas outlet-side end (for example, see Patent Literature 1).